Abstract
BackgroundMild cognitive impairment (MCI) is a common symptom in the patients with Parkinson’s disease (PD). The characteristics of cognitive impairment in PD are executive function (including working memory) and visuo-perceptual processing. The visuospatial n-back test has the merit of minimizing the influence of educational biases involved in the verbal n-back test. Furthermore, it can assess both visuospatial recognition and working memory in a single test.MethodsWe aimed to clarify the advantage of the visuospatial n-back test as a tool for detecting impairments of working memory in PD. We enrolled 28 right-handed patients with PD (18 males, 10 females) and 12 age-matched healthy controls (HC; 7 males, 5 females). Thirteen patients were classified as MCI (PD-MCI), and 15 as cognitively normal PD (PD-CN). Using functional MRI (fMRI), we explored the specific brain regions associated with the performance of the n-back test in the PD-MCI, PD-CN, and HC groups. The 0-back test assesses visuospatial recognition, while the 1-back and 2-back tests assess visuospatial working memory. Group comparisons were performed for three loads of this test.ResultsPatients with PD performed significantly worse in terms of the correct answer rates of all n-back tests compared with HC. fMRI analyses performed during the 2-back test revealed reduced activation in the bilateral dorsolateral prefrontal cortex, middle frontal gyrus (MFG), and parietal lobule in the PD group compared with the HC group. In contrast, the fMRI result during the 0-back test showed only a marginal difference in the frontal lobe. On comparisons of task performance between the PD-MCI and PD-CN groups, we found that the correct answer rate in the 2-back test was lower in the PD-MCI group than in the PD-CN group. However, scores of the 0-back and 1-back tests were not significantly different between the two groups. The fMRI findings revealed that activations within the middle frontal gyrus (MFG) and inferior parietal lobule (IPL) during the 2-back test were reduced in the patients with PD-MCI when compared to those with PD-CN.ConclusionsThis study reports reduced activation of the MFG and IPL in patients with PD-MCI. These regions may be associated with the pathophysiology of working memory impairment in patients with PD, which involves fronto-striatal network dysfunction.
Highlights
Striatal dopamine depletion due to the degeneration of nigrostriatal dopaminergic neurons causes motor disturbances in the patients with Parkinson’s disease (PD)
The movement disorder society (MDS) has published the clinical criteria for dementia in PD (PDD) in 2007 [1], and the MDS Task Force has provided the criteria for mild cognitive impairment (MCI) in PD (PD-Mild cognitive impairment (MCI)) in 2012 [2]
To assess the influence of aging on visuospatial working memory in normal subjects, several functional MRI (fMRI) studies have used the visuospatial version of the n-back task as well as the verbal n-back task [16, 17]. Considering these studies, we focused on this test because it has two advantages for the cognitive assessment of patients with PD: first, the merit of minimising the influence of educational biases or differences in native language, such as those found in the verbal n-back test; and second, it simultaneously assesses visuospatial recognition in a single test
Summary
Striatal dopamine depletion due to the degeneration of nigrostriatal dopaminergic neurons causes motor disturbances in the patients with Parkinson’s disease (PD). The movement disorder society (MDS) has published the clinical criteria for dementia in PD (PDD) in 2007 [1], and the MDS Task Force has provided the criteria for mild cognitive impairment (MCI) in PD (PD-MCI) in 2012 [2]. The different criteria produce different classifications of PD-MCI status, both assessment (based on abbreviated and comprehensive criteria), are needed to evaluate cognitive impairment of the PD. Mild cognitive impairment (MCI) is a common symptom in the patients with Parkinson’s disease (PD). The visuospatial n-back test has the merit of minimizing the influence of educational biases involved in the verbal n-back test. It can assess both visuospatial recognition and working memory in a single test
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